1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to devices and methods for performing minimally invasive direct cardiac massage.
Sudden cardiac arrest is a leading cause of death in most industrial societies. While in many cases it is theoretically possible to re-establish cardiac function, irreversible damage to vital organs, particularly the brain and the heart itself, will usually occur prior to restoration of normal cardiac activity.
A number of techniques have been developed to provide artificial circulation of blood to oxygenate the heart and brain during the period between cardiac arrest and restoration of normal cardiac activity. Prior to the 1960's, open chest cardiac massage (OCM) was a standard treatment for sudden cardiac arrest. Open chest cardiac massage, as its name implies, involved opening a patient's chest and manually squeezing the heart to pump blood to the body. In the 1960's, closed chest cardiac massage (CCM) where the heart is externally compressed through the chest wall became the standard of treatment. When CCM is combined with airway support, it is known as cardiopulmonary resuscitation (CPR). CPR has the advantage that it is much less invasive than OCM and can be performed by less skilled individuals. It has the disadvantage, however, that it is not generally effective. In particular, the medical literature shows that CCM provides significantly less cardiac output, neuroperfusion, and cardiac perfusion than achieved with OCM.
Methods and devices for performing minimally invasive direct cardiac massage have been described by Buckman et al. and by Drs. Filiberto and Giorgio Zadini in the patent and literature publications listed in the Description of the Background Art below. While the methods of Buckman et al. and the Zadinis differ in a number of respects, they generally rely on introducing a balloon, shoe, or other deployable member to engage the heart through a small incision through an intercostal space above the pericardium. The heart may then be pumped by directly engaging and compressing the pericardium, either by inflating and deflating the member or by reciprocating a shaft attached to the member. Although these approaches have been shown to be effective in animal models, the particular devices described in the patents are awkward for emergency use on human patients. In particular, the balloon-type and shoe-type heart-engaging members described in the patents may be difficult to deploy in the potential space between the posterior surface of the rib cage and the pericardium. For example, inflatable balloon members may lack sufficient rigidity to impart the necessary compressive force, rigid shoe-like members risk damage to the pericardium, and cup-shaped compressive members may compress so much of the heart volume that the end diastolic volume is compromised.
For these reasons, it would be desirable to provide improved methods and devices for performing minimally invasive direct cardiac massage. In particular, it would be desirable to provide apparatus and methods which are simple to deploy and carry out and in particular which do not require intervention by a physician. The heart-engaging component(s) of the devices should reliably deploy and expand within the region between the posterior rib cage and the pericardium and should minimize risk to the pericardium from perforation and other damage. The devices and methods should be simple to introduce to the patient in the first place, and in at least some circumstances, should eliminate the need to separately make an incision before introducing the device. The apparatus and method further should be compatible both with manual actuation, i.e., manual reciprocation of a handle or shaft attached to the heart-engaging member, and with automatic or powered systems for reciprocating the member. At least some of these objectives will be met by the invention described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 5,582,580, 5,571,074 and 5,484,391 to Buckman, Jr. et al. and 5,683,364 and 5,466,221 to Zadini et al., licensed to the assignee of the present application, describe devices and methods for minimally invasive direct cardiac massage through an intercostal space. Published PCT application WO 98/05289 and U.S. Pat. No. 5,385,528 describe an inflatable device for performing direct cardiac massage. U.S. Pat. No. 3,496,932 describes a sharpened stylet for introducing a cardiac massage device to a space between the sternum and the heart. Cardiac assist devices employing inflatable cuffs and other mechanisms are described in U.S. Pat. Nos. 5,256,132; 5,169,381; 4,731,076; 4,690,134; 4,536,893; 4,192,293; 4,048,990; 3,613,672; 3,455,298; and 2,826,193. Dissectors employing inflatable components are described in U.S. Pat. Nos. 5,730,756; 5,730,748; 5,716,325; 5,707,390; 5,702,417; 5,702,416; 5,694,951; 5,690,668; 5,685,826; 5,667,520; 5,667,479; 5,653,726; 5,624,381; 5,618,287; 5,607,443; 5,601,590; 5,601,589; 5,601,581; 5,593,418; 5,573,517; 5,540,711; 5,514,153; and 5,496,345. Use of a direct cardiac massage device of the type shown in the Buckman, Jr. et al. patents is described in Buckman et al. (1997) Resuscitation 34:247-253 and (1995) Resuscitation 29:237-248.